netdev - followup: what's responsible for setting netdev->operstate to IF_OPER

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Date:   Sun, 26 Aug 2018 11:14:33 -0400 (EDT)
From:   "Robert P. J. Day" <rpjday@...shcourse.ca>
To:     Linux kernel netdev mailing list <netdev@...r.kernel.org>
Subject: followup: what's responsible for setting netdev->operstate to
 IF_OPER_DOWN?

  apologies for the constant pleas for assistance, but i think i'm
zeroing in on the problem that started all this. recap: custom
FPGA-based linux box with multiple ports, where the current symptom is
that there is no userspace notification when someone simply unplugs
one of the ports ("ifconfig" shows that interface still RUNNING).

  as i read it, an active ethernet interface should be both UP (the
administrative state) and RUNNING (the RFC 2863-defined operational
state). if i unplug, i've verified on a standard net port on my laptop
that the interface is still UP, but no longer RUNNING, which makes
perfect sense. i plug back in, interface starts RUNNING again. so
where's the problem?

  i can see that whether ifconfig shows an interface RUNNING is
defined in net/core/dev.c:

  unsigned int dev_get_flags(const struct net_device *dev)
  {
        unsigned int flags;

        flags = (dev->flags & ~(IFF_PROMISC |
                                IFF_ALLMULTI |
                                IFF_RUNNING |
                                IFF_LOWER_UP |
                                IFF_DORMANT)) |
                (dev->gflags & (IFF_PROMISC |
                                IFF_ALLMULTI));

        if (netif_running(dev)) {
                if (netif_oper_up(dev))
                        flags |= IFF_RUNNING;  <---- THERE
                if (netif_carrier_ok(dev))
                        flags |= IFF_LOWER_UP;
                if (netif_dormant(dev))
                        flags |= IFF_DORMANT;
        }

        return flags;
  }

where netif_oper_up() is defined as:

  static inline bool netif_oper_up(const struct net_device *dev)
  {
        return (dev->operstate == IF_OPER_UP ||
                dev->operstate == IF_OPER_UNKNOWN /* backward compat */);
  }

so i am simply assuming that the underlying problem is that,
somewhere down below, the unplugging of a port is somehow not setting
dev->operstate to its proper value of IF_OPER_DOWN.

  that would clearly explain everything, and i'm about to dig even
further to see where the event of unplugging a port *should* be
recognized, but does this sound like a reasonable diagnosis? there
have been other problems with the programming of the FPGA, so it would
surprise absolutely no one to learn that this aspect was
misprogrammed.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                  http://crashcourse.ca/dokuwiki

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================